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1. Field of the Invention
The invention relates to improvements made to radial turbomachines of the type comprising at least one centripetal radial turbine comprising a rotor mounted to rotate in a casing about an axis of rotation, the rotor comprising a disk that can rotate about its axis which is coincident with the axis of rotation, and in which a face of the disk facing in the downstream direction with respect to the direction of flow of a fluid let into the turbine is fitted with blades.
2. Background Art
Centripetal radial and radial-axial turbines of the state of the art generally comprise, from the upstream to the downstream end, an inlet volute, a plain (that is to say unbladed) nozzle with fixed walls, followed by a bladed centripetal radial rotor or a radial-axial rotor when the stream flowing through the rotor changes from the radial direction to the axial direction, and finally a plain and generally axial oriented exhaust diffuser.
In a configuration of such a turbine with a low cross section, according to a known alternative form, the turbine has no inlet volute, and inlet is via an axial-centripetal radial duct of revolution about the axis of rotation. According to another known alternative form, a bladed nozzle is arranged between the inlet volute or the axial-radial inlet duct and the plain nozzle.
Furthermore, the rotor disk, in the inlet region, has significant notches or apertures between the blades, and this makes it possible to reduce the stresses in the rotor and its inertia.
These known centripetal radial and radial-axial turbines have the following disadvantages: their plain nozzle has a radius ratio (outside radius/inside radius) generally higher than 1.1, so as to limit the erosion of the trailing edges of the blades of the bladed nozzle, this erosion being due to the centrifuging of particles. In the absence of a bladed nozzle, the radius ratio of the plain nozzle is very high, because this radius ratio governs the acceleration of the fluid. As the speed of the fluid leaving the plain nozzle is high, the length of the stream lines is long, the coefficient of friction is not insignificant, and the hydraulic diameter small, this means that losses of stagnation pressure by viscosity may be significant in the plain nozzle.
Furthermore, in the rotor and more specifically at the notches thereof, the frictional losses are once again not insignificant, because the friction rate to be considered is the rate of flow with respect to the fixed casing, that is to say a rate similar to the rate at which the rotor rotates.
Finally, at the exhaust, and more specifically in the case of non-optimum operation (away from the nominal point), the axial exhaust diffuser does not allow the tangential kinetic energy to be converted into pressure. This is rendered possible by the use of a radial exhaust diffuser with fixed walls. However, in the latter instance, the tangential friction greatly diminishes the pressure gains that could theoretically be achieved by the use of such a component.
One object of the invention is to improve the overall efficiency of this type of turbomachine by improving their inlet and, preferably also, or alternatively, their exhaust.
Another object of the invention is to combine, within such a radial turbomachine, a centrifugal compressor with the centripetal turbine according to the invention so as to obtain a turbocompressor unit the respective inlets and/or exhausts of which are perfected, so as to improve the overall efficiency of the turbocompressor unit thus obtained by comparison with similar units of the state of the art, and in particular by limiting the axial bulk of such a unit at the cost of a limited increase both in the cross section and the weight and structural complexity of such a turbocompressor unit.
Yet another object of the invention is to propose a turbomachine with a centripetal radial turbine and, possibly, centrifugal radial compressor, which can be produced by using two-dimensional machining techniques, of the microelectronic type.
The field of application at which the invention is targeted relates essentially to the microturbines, particularly of the type used for producing auxiliary power units for aircraft or for propelling unmanned aerial vehicles, such as microdrones.
To this end, the invention proposes a turbomachine comprising at least one centripetal radial turbine of the type set out hereinabove, and which is characterized in that the centripetal turbine is supplied with fluid by a plain radial inlet nozzle rotating freely and coaxially with respect to the turbine rotor and surrounding the turbine rotor.
One essential advantage afforded by the plain freely rotating radial nozzle is that it makes it possible to very significantly reduce the losses through friction on the walls of this member because the kinetic energy of the fluid in the movement associated with the walls is practically quartered. In the same way, at the apertures in the rotor, the presence of the rotary disk of the nozzle makes it possible to reduce the losses through friction of the fluid against the fixed casing, because the kinetic energy of the fluid in the movement associated with the walls is also quartered.
To improve performance, the turbomachine of the invention also and advantageously comprises at least one centrifugal radial compressor comprising a rotor coaxial with the turbine rotor and rotating as one with the turbine rotor about the axis of rotation in the casing, the compressor rotor comprising a rotary disk coaxial with the turbine rotor disk and of which a face facing in the upstream direction with respect to the direction of flow of a fluid let into the compressor is equipped with blades compressing the fluid toward a plain radial exhaust diffuser rotating freely and coaxially with respect to the plain and freely rotating radial turbine inlet nozzle, the compressor exhaust diffuser surrounding the compressor rotor and being surrounded by a fluid flow uptake volute in communication with a fluid inlet volute surrounding the turbine inlet nozzle, for supplying the latter through said inlet nozzle.
The function of the compressor plain radial exhaust diffuser is to convert some of the kinetic energy acquired by the fluid leaving the compressor wheel into a pressure increase, because of the increase in the radius or distance between the point in question and the axis of rotation of the machine, and because of the conservation of momentum, give or take the friction on the walls, this friction being reduced because this plain radial diffuser is mounted so that it can rotate freely. The presence of moving walls, both for the centrifugal compressor plain radial exhaust diffuser and for the centripetal turbine plain radial inlet nozzle makes it possible to appreciably reduce the aerodynamic losses through friction between fluid and walls in the two plain radial ducts passing one through the nozzle and the other through the diffuser, these aerodynamic losses being associated with the fact that there is significant momentum both on the compressor side and on the turbine side.
Advantageously, to improve the compactness and simplify the structure of the machine, and to further reduce the aerodynamic losses, the compressor plain radial exhaust diffuser and the turbine plain radial inlet nozzle are arranged as a single assembly free to rotate coaxially with respect to the turbine and compressor rotors.
In this architecture, it is advantageous for the freely rotating assembly to comprise an intermediate disk mounted so that it is free to rotate, between the turbine and compressor rotor disks, about a common main shaft connecting together the turbine and compressor rotor disks so that they rotate as one about the axis of rotation. Thus frictional losses at the rotor disks are also reduced because the intermediate disk is set in rotation between the turbine and compressor rotor disks.
In an advantageously simple and effective structural embodiment, the compressor plain and freely rotating radial exhaust diffuser has, passing through it, a radial duct delimited between two plain walls facing one another and of revolution about the axis of rotation, and of which one is a wall of a downstream disk coaxial with the compressor rotor and free to rotate about the axis of rotation independently of the compressor rotor, the other wall of the duct being a wall of an upstream annular ring coaxial with the compressor rotor and secured to the downstream disk of said exhaust diffuser so that it rotates as one therewith, by substantially axial spacer pieces in a substantially radially external position, with respect to the axis of rotation, on said upstream annular ring and on said downstream disk.
This structure, known per se, of a centrifugal compressor and of its plain radial exhaust diffuser rotating freely about the axis of rotation of the compressor rotor can be read across to the production of the centripetal turbine and of its plain radial inlet nozzle rotating freely about the axis of rotation of the turbine rotor, in a turbomachine according to the invention, to further improve the overall efficiency thereof.
As a result, according to the invention, the turbine plain and freely rotating radial inlet nozzle advantageously has, passing through it, a radial duct delimited between two plain walls facing one another and of revolution about the axis of rotation, and of which one is a wall of an upstream disk coaxial with the turbine rotor and free to rotate about the axis of rotation independently of the turbine rotor, the other wall of the duct being a wall of a downstream annular ring coaxial with the turbine rotor and secured to the upstream disk of said inlet nozzle so that it rotates as one therewith, by substantially axial spacer pieces in a substantially radially external position, with respect to the axis of rotation, on said downstream annular ring and on said upstream disk.
Thus, in the case of the compressor diffuser and in the case of the turbine nozzle, the moving equipment that is free to rotate and which consists of an annular ring, of a corresponding disk and of the spacer pieces which join them together so that they rotate as one, adopts a rotational speed corresponding to equilibrium between a driving torque, associated with the driving by the fluid in the radial duct of the exhaust diffuser or of the inlet nozzle and by the fluid trapped between the walls of the disk of the moving equipment in question, and of the corresponding compressor or turbine rotor disk, and a resistive torque which is due to the braking action exerted by the fluid trapped between the corresponding annular ring and the wall facing it belonging to the fixed casing of the machine.
Advantageously, when the architecture with a freely rotating disk secured by spacer pieces to an annular ring as specified hereinabove is adopted for the compressor exhaust diffuser and for the turbine inlet nozzle, it is advantageous for the freely rotating upstream disk of the turbine plain radial inlet nozzle and the freely rotating downstream disk of the compressor plain radial exhaust diffuser to rotate as one with the intermediate disk of the freely rotating assembly, and to be preferably of one single piece with said intermediate disk. The aerodynamic losses through friction between fluid and walls are thus further reduced while at the same time improving the compactness of the machine and reducing the number of its constituent parts, which constitutes a saving.
In order to further improve the overall efficiency of the machine, at the turbine, which may or may not collaborate with a centrifugal compressor, a fixed bladed nozzle may surround the turbine plain and freely rotating radial inlet nozzle and may itself be surrounded by the turbine inlet peripheral volute. If the turbomachine comprises a centrifugal compressor the rotor of which rotates as one with the rotor of the centripetal turbine, the overall efficiency of the machine can be further improved, at the compressor, using a fixed bladed diffuser which surrounds the compressor plain and freely rotating radial exhaust diffuser and which is itself surrounded by the fluid flow uptake peripheral volute.
According to another aspect of the invention, whether or not the turbomachine comprises a centrifugal compressor, the rotor of the centripetal turbine advantageously delivers the fluid flowing through said turbine to a plain and freely rotating radial exhaust diffuser rotating coaxially with respect to the turbine rotor in the casing.
Advantageously, this turbine plain radial and freely rotating exhaust diffuser may have the same overall architecture as the compressor plain radial and freely rotating exhaust diffuser and as the turbine plain and freely rotating radial inlet nozzle, as were defined hereinabove. In this case, the turbine plain and freely rotating radial exhaust diffuser also has, passing through it, a radial duct delimited between two plain walls facing each other and of revolution about the axis of rotation, of which one is a wall of a downstream disk coaxial with the turbine rotor and mounted so that it is free to rotate independently of the turbine rotor about the axis of rotation, for example, rotating as one with a tubular secondary shaft, guided in rotation by at least one bearing about a coaxial hub of the turbine exhaust diffuser, the other wall of the duct being a wall of an upstream annular ring coaxial with the turbine rotor and being secured to the freely rotating downstream disk of said turbine exhaust diffuser so as to rotate as one therewith by substantially axial spacer pieces and in a substantially radially external position on said upstream annular ring and said downstream disk of said turbine exhaust diffuser.
Although a plain and freely rotating radial nozzle is more difficult to produce than a plain and fixed axial exhaust nozzle, and requires in addition fluid flow to be taken up by a peripheral volute surrounding the plain and freely rotating radial nozzle, the fitting of the latter to the exhaust of a centripetal turbine does, by comparison with the fitting of a plain and fixed axial diffuser onto the exhaust of a centripetal turbine as is known in the state of the art, afford the advantages of allowing, apart from a saving on the axial bulk, a lowering of the tangential speed in the downstream direction, and therefore an increase in the static pressure which is greater than the one observed in an axial diffuser, which means in particular that the torque on the turbine shaft, during a start-up phase is higher, and the response time is shortened. The turbine radial exhaust diffuser therefore makes it possible to recuperate a higher proportion of the kinetic energy of the fluid than is possible with an axial diffuser, this making it possible to increase the efficiency of the turbine and obtain greater power on the shaft thereof. Furthermore, the reduction in the tangential speed in a turbine plain radial exhaust diffuser, followed by the recuperation of the fluid by a peripheral volute, has the significant advantage of leading to a quiet exhaust, unlike the situation encountered with a plain axial diffuser in which the concentration of a swirling flow near to the axis of rotation of the machine leads to there being, in this region, a core of xe2x80x9cdeadxe2x80x9d fluid and unsteady phenomena which are due to a shear between the xe2x80x9cdeadxe2x80x9d fluid and the xe2x80x9chealthyxe2x80x9d fluid, which is why there is a not insignificant noise level.
According to the invention, mounting the turbine plain radial exhaust diffuser so that it is free to rotate further increases the qualities of the machine, because of the reduction in the friction between the fluid and the walls of this diffuser, which means that the efficiency and the power of the centripetal turbine increase still further in non-optimized operation, particularly upon start-up, and that the noise level drops further, this being due to the lowering of the level of turbulence in the diffuser.
When the machine comprises a centrifugal compressor, as explained hereinabove, the overall efficiency is further improved by supplying the compressor with fluid through a plain radial nozzle rotating freely coaxially with respect to the compressor rotor, inside the casing.
In practical terms, this compressor plain and freely rotating radial inlet nozzle may be produced with the overall architecture of the centripetal turbine radial inlet nozzle and centripetal turbine and centrifugal compressor radial exhaust diffusers as were explained hereinabove. In particular, the compressor plain and freely rotating radial inlet nozzle may have, passing through it, a radial duct delimited between two plain walls facing each other and of revolution about the axis of rotation, of which one is a wall of an upstream disk coaxial with the compressor rotor and mounted so that it is free to rotate independently of the compressor rotor about the axis of rotation, for example, rotating as one with a tubular tertiary shaft, guided in rotation by at least one bearing about a coaxial hub of said compressor inlet nozzle, the other wall of the duct being a wall of a downstream annular ring coaxial with the compressor rotor and being secured to the freely rotating upstream disk of the compressor inlet nozzle so as to rotate as one therewith by substantially axial spacer pieces and in a substantially radially external position on said downstream annular ring and said upstream disk of said compressor inlet nozzle.
This plain and freely rotating radial nozzle for supplying the compressor is set in rotation because of the frictional torque due to there being momentum in the fluid passing through this radial nozzle, the equilibrium rotational speed of which is obtained for equilibrium between the abovementioned driving frictional torque and a resistive frictional torque created by the fluid trapped between the faces facing each other belonging to the upstream disk and to the downstream annular ring of this nozzle, on the one hand, and the casing, on the other hand. The free rotation of this plain radial nozzle makes it possible to reduce the aerodynamic losses in this region of the machine.
Advantageously also, this plain and freely rotating radial nozzle for supplying the compressor is surrounded by a fixed radial nozzle with orientable or variable-pitch blades which can be adjusted when there is a desire to vary the flow rate and the compression ratio of the machine, particularly in the case of air-conditioning compressors and those used for refrigeration. Indeed it should be noted that the centrifugal compressor as defined hereinabove, preferably with its plain and freely rotating radial exhaust diffuser and a peripheral volute for taking up the flow of fluid, possibly with the interposition of a bladed fixed radial diffuser surrounded by this volute and surrounding the plain and freely rotating radial diffuser and with a compressor plain and freely rotating radial inlet nozzle, possibly preceded by a fixed radial nozzle with orientable blades surrounding the plain and freely rotating radial nozzle, constitutes a centrifugal compressor that can be used in isolation, independently of any centripetal turbine, and which has a novel structure by comparison with the centrifugal compressors of the state of the art and affords particularly appreciable advantages over the latter. Such a centrifugal compressor as defined hereinabove therefore in itself constitutes an invention.
When the turbomachine is a turbocompressor with a turbine plain freely rotating radial exhaust diffuser and with a compressor plain and freely rotating radial inlet nozzle, the turbine and compressor rotors can rotate as one with one another on coaxial journals about the axis of rotation and between the hubs of the turbine plain radial exhaust diffuser and the compressor plain radial inlet nozzle. However, in the case of an arrangement as a gas turbine, in which power output is required from the turbine shaft, the turbine and compressor rotors can rotate as one with the hub of the turbine free radial exhaust diffuser, said diffuser hub being mounted so that it can rotate coaxially about the axis of rotation in the casing via at least one additional bearing, while the turbine and compressor rotors and the turbine plain radial exhaust diffuser rotary hub are mounted so that they rotate on the fixed hub of the compressor plain radial inlet nozzle via, for example, a journal coaxial with the axis of rotation.
Other features and advantages of the invention will become apparent from the description given hereinbelow of some non-limiting exemplary embodiments described with reference to the appended drawings.